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Pollution control

A Fungus that Decontaminates Soil

Using a fungus that is able to degrade pesticide derivatives, researchers have found a promising means of remediating cultivated land.

After several decades of modern intensive farming, much research is now aimed at purging our soils of numerous substances of industrial origin. One promising solution may come from an ordinary filamentous fungus, Podospora anserina.1 A collaborative study2 led by Philippe Silar (IGM) and Jean-Marie Dupret (BFA) has shown that Podospora anserina is indeed capable of “digesting” pollutant molecules by chemically modifying them, using one of its enzymes. Indeed, where another living species might have perished, this fungus assimilates the pollutant and transforms it into a harmless substance, thus remediating the environment.
fungus

© P. Sila

After fertilization, Podospora anserina develops fruiting bodies (small furry pear-shaped outgrowth about 0.75 mm long) that protect the reproduction events.



Because fungi constitute a remarkable reservoir of enzymes with astonishing properties, the scientists decided to test the resistance of several species of molds to a major class of pollutants, aromatic amines. Two of them survived, indicating that these fungi are endowed with enzymes that allow them to “digest” these aromatic amines. The researchers chose to focus their efforts on Podospora anserina, which is already well-known to research, and whose genome has been entirely sequenced. They were able to identify, clone, and purify an enzyme involved in these resistance mechanisms: PaNAT2. To define its role more precisely, Silar's team produced mutated strains in which the gene for the PaNAT2 enzyme was inactivated, and challenged them with a derivative of a pesticide found in some types of agricultural land, 3,4-dichloroaniline (3,4-DCA). In a liquid medium, about 45% of the pollutant was degraded by the normal strain of Podospora anserina after 3 days, versus only 5% by the mutated strain of the fungus. “This proves unambiguously that the PaNAT2 enzymatic pathway is involved in the ability of this fungus to tolerate certain aromatic molecules,” explains Dupret.
The scientists then tested the remediation (i.e., soil decontamination) capacity of the fungus. They planted lettuce seeds (known for their sensitivity to 3,4-DCA) in a soil containing the pollutant, but which had been treated with the fungus for three days. The salad seeds germinated normally, even at an extremely high concentration of the pollutant, thus proving irrefutably the remediation capacity of Podospora anserina. This fungus presents another considerable advantage as a candidate for soil remediation: it multiplies by sexual reproduction. To prevent its uncontrollable proliferation, simply inoculating strains of only one mating type will make the fungus disappear after a certain period of time.
However, before field-scale trials can begin, the team needs to answer a few questions: How can the fungus be produced in large quantities? Does it need to be buried, or can it just be spread on the soil surface? Only once they have the results of these preliminary experiments will the scientists consider testing the method under real-life conditions.

Caroline Dangléant

Notes :

1. M. Martins et al., “An acetyltransferase conferring tolerance to toxic aromatic amine chemicals: molecular and functional studies,” J Biol. Chem., 2009. 284: 18726-33.
2. Unité de Biologie Fonctionnelle et Adaptative (BFA) (CNRS / Université Paris-VII); Institut de Génétique et Microbiologie (IGM) (CNRS / Université Paris-XI); Interfaces, traitements, organisation et dynamique des systèmes (ITODYS) (CNRS / Université Paris-VII).

Contacts :

Jean-Marie Dupret,
Unité BFA, Paris.
jean-marie.dupret@univ-paris-diderot.fr


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